Method for purification of acarbose

ABSTRACT

The present invention relates to a novel process for the preparation of acarbose. Said process comprises the steps of: 1) acidifying a fermentation broth containing an acarbose; 2) removing particulates from the fermentation broth; 3) adsorbing the acarbose on a cation-exchanger in the presence of an anion of a weak acid; 4) eluting the acarbose from the cation-exchanger with at least one of a sodium chloride solution and a salt solution; 5) precipitating the acarbose with a solvent; and 6) recovering the precipitated acarbose.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This is a continuation-in-part application of the U.S.Conventional application Ser. No. 09/924,271 filed on Aug. 7, 2001 whichclaims the benefit of the Provisional Application Serial No. 60/223,492filed Aug. 7, 2000, the disclosures of which are incorporated byreference in their entireties herein.

FIELD OF THE INVENTION

[0002] The present invention relates to a novel process for thepurification of acarbose.

BACKGROUND OF THE INVENTION

[0003] Acarbose, also known as O-4,6-Dideoxy-4[[[1S-(1α, 4α, 5β,6α)]-4,5,6-trihydroxy-3-(hydroxmethyl)-2-cyclohexen-1-yl]amino]-α-D-glycopyranosyl-(1→4)-O-α-D-glucopyranosyl-(1→4)-D-glucose,or 4″,6″-dideoxyl-4″-[(1S)-(1,4,6/5)-4,5,6-trihydrox-3-hydroxymethyl-2-cyclohexenylamino]maltotriose,has the following formula (I).

[0004] Acarbose is a potent α-glucosidase inhibitor that reduces sugarabsorption in the gastrointestinal tract. It is used as an orallyadministered anti-diabetic drug sold under the trademark GLUCOBAY® andis available for the treatment of diabetes mellitus in humans.

[0005] U.S. Pat. No. 4,062,950 and Ger. Pat. No. 2,347,782 describe theisolation of acarbose from strains of Actinoplanes. These processesemploy the use of ion-exchangers to adsorb acarbose from fermentationbroths; but the ion-exchange steps contain nitrate anion. The presenceof nitrate anion causes impurities to adsorb onto the ion-exchangeresins and thus contaminates the acarbose. The presence of impuritiesalso complicates the purification process because additionalpurification steps are needed to remove these impurities.

[0006] There is a need for an improved process for purification foracarbose. It is desirable to develop a purification process for acarbosewhereby an increased purity of acarbose can be obtained with simplifiedpurification steps.

SUMMARY OF THE INVENTION

[0007] According to one aspect, the present invention provides a processfor the purification of acarbose using ion-exchange chromatography;specifically, a cation-exchanger; and more specifically, acation-exchanger in the presence of a weak acid.

[0008] According to another aspect, the present invention involves theuse of a strong cation-exchanger in the presence of an anion of a weakacid to adsorb acarbose.

[0009] The present invention provides a method of purifying acarbose,which comprises the steps of:

[0010] 1) acidifying a fermentation broth containing an acarbose;

[0011] 2) removing particulates from the fermentation broth;

[0012] 3) adsorbing the acarbose on a cation-exchanger in the presenceof an anion of a weak acid;

[0013] 4) eluting the acarbose from the cation-exchanger with at leastone of a sodium chloride solution and a salt solution;

[0014] 5) precipitating the acarbose with a solvent; and

[0015] 6) recovering the precipitated acarbose.

[0016] The present invention provides a method of purifying acarbose,which comprises the steps of:

[0017] 1) acidifying a fermentation broth containing an acarbose;

[0018] 2) removing particulates from the fermentation broth;

[0019] 3) adsorbing the acarbose on an anion-exchanger in the presenceof an anion of a weak acid;

[0020] 4) eluting the acarbose from the anion-exchanger;

[0021] 5) adsorbing the eluted acarbose on a cation-exchanger in thepresence of the anion of a weak acid;

[0022] 6) eluting the acarbose from the cation-exchanger with at leastone of a sodium chloride solution and a salt solution;

[0023] 7) precipitating the acarbose with a solvent; and

[0024] 8) recovering the precipitated acarbose.

DETAILED DESCRIPTION OF THE INVENTION

[0025] Definitions

[0026] As used herein, the term “anion” refers to a negatively-chargedion and the term “cation” refers to a positively-charged ion.

[0027] As used herein, “ion exchange chromatography” refers to aseparation method that employs charged ion-exchanger for binding andeluting a target molecule (e.g., acarbose).

[0028] As used herein, a “cation-exchanger” is a type of chargedion-exchanger that possesses a net negative charge which binds acarbose.One skilled in the art will appreciate that a strong ion-exchanger isone which remains almost fully ionized over a wide pH range whereas aweak exchanger is ionized over a small pH range. The terms “strongcation-exchanger” and “strong acid cation-exchanger” are usedinterchangeably and they refer to the same types of cation-exchangers.

[0029] As used herein, the term “a salt solution” refers to a solutionat least one of chloride salt, sulfate salt, nitrate salt, acetate saltand the like.

[0030] As used herein, “a solution of chloride salt” refers to sodiumchloride, potassium chloride, calcium chloride and the like.

[0031] As used herein, “a solution of sulfate salt” refers to sodiumsulfate, potassium sulfate, calcium sulfate and the like.

[0032] As used herein, “a solution of nitrate salt” refers to sodiumnitrate, potassium nitrate, calcium nitrate and the like.

[0033] As used herein, “a solution of acetate salt” refers to sodiumacetate, potassium acetate, calcium acetate and the like.

[0034] Among the strong acid cationic exchange resins which may be usedare those having sulfonic acid (SO3⁻H⁺) groups. These include commercialproducts, e.g., Amberlite® IR-118, IR-120, 252H; Amberlyst® 15, 36;Amberject® 1200 (H) (Rohm and Haas); Dowex® 50 wX series, Dowex® HCR-W2,Dowex® 650C, Dowex® Marathon C, Dowex® DR-2030, and Dowex® HCR-S, ionexchange resin (Dow Chemical Co.); Diaion® SK 102 to 116 resin series(Mitsubishi Chemical Corp.) and Lewatit SP 120 (Bayer). The preferredstrong acid cationic exchange resins are Amberlite® 120, Dowex® 50 WXand Diaion® SK series.

[0035] Preferred cation-exchangers also include Amberlite®. Amerbliteion-exchanger employs a polystyrene resin matrix. Amberlite® 252 resinin H⁺ form is an example for cation-exchanger in acid form. Preferredcation-exchanger is Amberlite® 252 in H⁺ form.

[0036] Cation ion-exchangers further include sulpho, sulphomethyl (i.e.,methyl sulfonate), and sulphopropyl forms. Preferable cation-ionexchangers include the functional group of methyl sulfonate. Exemplarystrong cation-exchangers include Mini S® (methyl sulfonate), Mono S®(methyl sulfonate), SP Sepharose® (methyl sulfonate), SOURCE 15S®, 30S®(methyl sulfonate) and the like.

[0037] Weak cation ion-exchange resins include those which havecarboxylic acid groups as well as carboxy and carboxymethyl forms.Preferable weak cation-exchangers include the functional group of —COOH.An exemplary weak cation-exchanger is CM Sepharose Fast Flow®.

[0038] As used herein, an “anion-exchanger” refers to anion-exchangeresins that possess a net positive charge. Preferred anion-exchangeresins include resins that contain a quarternary amine functional group.Diethylaminoethyl (DEAE) exchangers and carboxymethyl (CM) exchangersare usually used as anion exchangers.

[0039] As used herein, the term “an anion of a weak acid” refers to ananion of organic acids or phosphate. The anion of weak acid is selectedfrom the group consisting of tartarate, succinate, citrate, acetate,formate, malonate, oxalate, phthalate, benzoate and phosphate.

[0040] As used herein, the term “weak acid” specifically refers to anacid selected from the group consisting of tartaric acid, succinic acid,citric acid, acetic acid, formic acid, malonic acid, oxalic acid,phthalic acid, benzoic acid and phosphoric acid.

[0041] As used herein, the term “particulates” refers to cellular debrisand other particles that are present in a fermentation broth.Particulates also include mycelium.

[0042] As used herein, the term “M” refers to a molar concentration inmoles/liter.

[0043] As used herein, the yield % is based on w/w. Each peak has anarea on a HPLC chromatogram. “Area %” refers to the peak area ofpurified product divided by the total area of all peaks multiplied by100.

[0044] As used herein, the term “yield of anion exchange” (See Table 1)refers to the yield % of acarbose prior to the cation-exchange step.

[0045] As used here, the term “summarized yield” refers to yield ofanion-exchange multiplied by yield of cation-exchange.

[0046] According to one embodiment, the present invention provides apurification process for acarbose employing an appropriate anion whichis selected from the group consisting of tartarate, succinate, citrate,acetate, formate, malonate, oxalate, phthalate, benzoate, and phosphate.

[0047] According to another embodiment, the present invention provides aprocess of purifying acarbose employing the presence of an anion of aweak acid during the cation-exchanger. When the anion of a weak acid ispresent, it is found that the impurities present in the fermentationbroth cannot adsorb onto the strong acid cation-exchanger. Consequently,only acarbose adsorbs onto the strong acid cation-exchanger, and resultsin a better purification. This results in selective adsorption ofacarbose. Accordingly, we found a novel phenomenon that adsorption ofacarbose without the impurities.

[0048] According to another embodiment, the present invention providesthe acarbose adsorbing onto a strong acid cation-exchanger withoutprevious desalting. In contrast, when counter-ions such as chloride,nitrate and the like are used, it is found that desalting is required.

[0049] According to another embodiment, the present invention providesan unexpected phenomenon where it is found that the specific type ofanion can influence the selectivity and adsorption capacity of thecation-exchanger.

[0050] According to another embodiment, the present invention provides aprocess for purifying acarbose employing the use of multipleion-exchangers. Fermentation broth is allowed to adsorb onto multipleion-exchangers successively. In particular, acarbose is eluted from ananion-exchanger prior to the adsorption onto a cation-exchanger. The useof successive exchangers has proved to be effective in purifyingacarbose.

[0051] A preferred embodiment for an anion-exchanger is ananion-exchanger where its resin is in OH⁻ form.

[0052] A preferred embodiment for an anion that is used in theanion-exchange is an anion that includes tartarate, succinate, citrate,acetate, formate, malonate, oxalate, phthalate, benzoate, and phosphate.

[0053] A preferred embodiment for an cation-exchanger is a strongcation-exchanger. The presently most preferred embodiment includes acation-exchanger that is a strong cation exchange resin in acid form.

[0054] According to another embodiment, the present invention employs acation-exchanger whereby a strong cation-exchanger resin is in calciumform.

[0055] According to another embodiment, the particulates present in thefermentation broth are removed. The techniques to remove theparticulates includes the sedimentation as well as filtering as one ofskill in the art would appreciate. Fermentation broth containingacarbose can be filtered prior to the application onto thecation-exchangers. The filtration of fermentation broth removes anyparticulates and cell debris. Preferably, the filter is a pre-coatvacuum drum filter. One skilled in the art would appreciate the use ofother filters of a similar kind and can serve a similar function as topre-clear the fermentation broth prior to the chromatographypurification. Most preferably, the filtration of fermentation broth isrepeated at least twice.

[0056] According to another embodiment, the fermentation brothcontaining acarbose is adjusted to an acidic pH prior to filtration.Preferably, prior to the first filtration, the pH of the fermentationbroth is adjusted to a pH of about 4.0 to a pH of about 6.0 with amineral acid or a weak acid.

[0057] A “mineral acid” is defined herein as a strong acidic solutionsuch as hydrochloric acid, sulphuric acid, nitric acid, phosphoric acidand the like.

[0058] A “weak acid” is selected from the group consisting of tartaricacid, succinic acid, citric acid, acetic acid, formic acid, malonicacid, oxalic acid, phthalic acid, benzoic acid, and phosphoric acid. Apreferred embodiment for a weak acid is acetic acid.

[0059] According to another embodiment, the present invention relates toa process of purifying acarbose using two ion-exchangers. Preferably,the first ion-exchanger is an anion-exchanger. Most preferably, thefirst anion-exchanger is in the acetate, tartarate or succinate forms.

[0060] Preferably, the second ion-exchanger is a strongcation-exchanger. Most preferably, the second cation-exchanger is astrong cation-exchanger in acid form.

[0061] According to another embodiment, the present invention relates toa process of purifying acarbose, wherein acarbose adsorbed onto acation-exchanger is eluted with either hydrochloric acid or weak acids.

[0062] According to another embodiment, the present invention relates toa process of purifying acarbose, wherein acarbose that is adsorbed ontoa cation-exchanger is eluted with either a sodium chloride solution or asalt solution of sulfate, nitrate or acetate.

[0063] According to another embodiment, the present invention relates toa process of purifying acarbose with an increased yield. Particularly,the invention provides eluting adsorbed acarbose from a cation-exchangerwith a salt solution wherein the yield of ion-exchange purification ishigher. Typically, the yield is higher than 85%.

[0064] According to another embodiment, the present invention relates toa process of purifying acarbose, wherein a solvent is used for theprecipitation of acarbose from the eluant. Preferably the solventincludes alcohol, a mixture of alcohols and acetone, acetonitrile, esterof acetic acid, ester of formic acid, ester of propionic acid or thelike.

[0065] The present invention is described in further detail withreference to the following examples. However, the present invention isby no means restricted to these specific examples.

EXAMPLES Example 1

[0066] A fermentation broth of 122 kg was acidified with sulfuric acidto about pH 4.0-4.5. The acidified fermentation broth was filtered onpre-coat vacuum drum filter. The filtered mycelium was washed withwater. The fermentation broth contained 537 gram active substance. Thefiltration yield was 91% (w/w). The volume of the filtrate was 227liters.

[0067] The pH of the acidified filtrate was adjusted to about 2.0-2.2with sulfuric acid and it was filtered again pre-coat drum filter. Thevolume of the filtrate was 223 liters. The filtration yield was 94%(w/w).

[0068] The pH of the filtrate of about 2.0-2.2 was adjusted to about4.0-7.0 with anion-exchange resin in basic form. The yield of the pHadjust was 94.5% (w/w).

[0069] The adjusted filtrate was poured through on ion-exchange column.The ion-exchange column contained 20 liters anion-exchange resin inacetate form. The flow rate was 12.5 liters/hour. The effluent flow wasconducted without desalinating continuously to another ion-exchangecolumn containing 22 liters strong acid cation-exchanger in acid form.The ion-exchange was finished with 50 liters rinsing water.

[0070] The active substance that were bound or adsorbed onto theion-exchange resin was eluted with 0.02 M hydrochloric acid. The eluantswere collected into different fractions using a fraction collector. Amain fraction of the eluants contained 374 gram active substance. Thevolume of the main fraction was 37.5 liters.

[0071] The summarized yield of the adsorption and elution was 87% (w/w).

[0072] The main fraction was analyzed by HPLC. HPLC method was asfollows: Supercoil LC-NH₂ column; 5 μM; mobile phase: 1.2 gram KH₂PO₄and 0.7 gram Na₂HPO₄ in 1,000 mL water; detection: UV2=210 nm. There wasless than 10% related substances on HPLC. The pH of the main fractionwas adjusted to about 4.0-5.0 with anion-exchange resin in basic form.

Example 2

[0073] Another purification of acarbose was performed with the followingprocedures.

[0074] A part (480 mL) of the pH adjusted main fraction was taken forpurification. This fraction contained 4.9 gram acarbose.

[0075] Two ion-exchange columns connected in series were used.

[0076] The first ion-exchange column contained 60 ml anion-exchangeresin in tartarte form. The second column contained 60 ml strong acidcation-exchanger in acid form. The applied flow rate was 40 ml/hour. Theion-exchange was finished with 120 mL rinsing water.

[0077] The adsorbed active substance was eluted from the second columnwith 0.02 M hydrochloric acid. The main fraction contained 4.4 gramacarbose. The main fraction was analyzed by HPLC. There were less than2% related substances on the HPLC chromatogram. The main fraction wasconcentrated after removing chloride ions with anion exchange resin inbasic form. The concentration of acarbose was about 50% (w/w).

[0078] The acarbose was precipitated in the presence of ethanol. Thecrystals were filtered and dried. The 4 gram product contained less than1% related substances.

Example 3

[0079] Another purification of acarbose was performed with the followingprocedures.

[0080] A part (480 mL) of the pH adjusted main fraction (final solutionof Example 1) was taken for purification. This part contained 4.8 gramacarbose.

[0081] Two ion-exchange columns connected in series were used.

[0082] The first ion-exchange column contained 60 mL anion-exchangeresin in succinate form. The second column contained 60 mL strong acidcation-exchanger in acid form. The applied flow rate was 40 mL/hour. Theion-exchange was finished with 120 mL rinsing water.

[0083] The adsorbed active substance was eluted from the second columnwith 0.02 M hydrochloric acid. The main fraction contained 4.3 gramsacarbose. The main fraction was analyzed with HPLC analysis method.There were less than 2% related substances on the HPLC chromatogram. Themain fraction was concentrated after removing chloride ions with anionexchange resin in basic form. The concentration of acarbose was about50% by w/w.

[0084] The acarbose was precipitated in the presence of ethanol. Thecrystals were filtered and dried. The 3.9 gram product contained lessthan 1% related substance.

Example 4

[0085] The purification of acarbose illustrated in the above-mentionedExample 1 were using strong ion-exchanger in the presence of an anion ofweak acids such as acetate, tartarte or succinate.

[0086] We found that other anion of weak acids can also influence thepurification of acarbose during the ion-exchange chromatography. Table 1summarizes the comparison of the efficiency of other anion of weakacids. Before the step of adsorbing acarbose onto the cation-exchanger,an anion exchanger was used to change the anion content of the filtratefrom an existing anion (a stronger anion such as sulphate, chloride,nitrate and the like) to an anion of a weak acid.

[0087] Optimal effects of other anion of weak acids on thecation-exchange chromatography in acarbose purification is seen in Table1.

Example 5

[0088] A fermentation broth of 60 kg was acidified with acetic acid topH about 4.0-6.0. Acid was added to fermentation broth and mixed. Theacidified fermentation broth was filtered on pre-coat vacuum drumfilter. The filtered mycelium was washed with water. The fermentationbroth contained 160 gram active substance. The filtration yield was 91%(w/w) using a HPLC method. The volume of the filtrate was 88 litres.

[0089] The filtrate was poured through on ion-exchange column. Theion-exchange column contained 8 litres strong acid cation-exchanger inacid form (Ambelite® 252 in H⁺ form). The ion-exchange was finished with8 litres rinsing water.

[0090] The active substance that were bound or adsorbed onto theion-exchange resin was eluted with 0.02 M hydrochloric acid. Theflow-rate was 1 liter/hour. Preferred solution is hydrochloric acid.Preferred concentration is 0.0002 M -0.03 M. Most preferredconcentration is 0.005 M-0.02 M. The eluants were collected intodifferent fractions using a fraction collector. A main fraction of theeluants contained 124 gram active substance.

[0091] The yield of ion-exchange purification process was 85% w/w asdetermined by HPLC.

[0092] The main fraction was analyzed by HPLC. Acarbose had a purity of94.5 area %. There were less than 10% impurity content. The details ofHPLC were as follows: HPLC column used: Supercosil LC-NH₂; particlesize: 5 μM; length: 250mm; diameter: 4.6 mm; mobile phase: 1.2 gramKH₂PO₄ and 0.7 gram Na₂HPO₄ in 1,000 mL water (pH: 6.5); injectionvolume: 20 μL; and detection: UV2=210 nm.

Example 6

[0093] A fermentation broth of 150 kg was acidified with acetic acid topH about 4.0 to about 6.0. Acid was added to fermentation broth andmixed. The acidified fermentation broth was filtered on pre-coat vacuumdrum filter. The filtered mycelium was washed with water. Thefermentation broth contained 927 gram active substance. The filtrationyield was 89% (w/w) using a HPLC method. The volume of the filtrate was246 litres.

[0094] The filtrate was poured through on ion-exchange column. Theion-exchange column contained 25 liters strong acid cation-exchanger inacid form. The flow rate was 9 liters/hour. The ion-exchange wasfinished with 40 liters rising water.

[0095] The active substance that was bound or adsorbed onto thecation-exchange resin was eluted with 0.002 M sodium chloride (NaCl)solution for 2 days, then with 0.1 M NaCl solution for 20 hours. Theeluants were collected into different fractions using a fractioncollector. A main fraction of the eluants contained 685 gram activesubstance.

[0096] The yield of ion-exchange purification process was 83.0% (w/w) asdetermined by HPLC.

[0097] The main fraction was analyzed by HPLC. Acarbose had a purity of96 area %.

[0098] It will be appreciated that the instant specification and claimsare set forth by way of illustration and not limitation, and thatvarious modifications and changes may be made without departing from thespirit and scope of the present invention. TABLE 1 ACARBOSE Effect ofanions of a weak acid on cation-exchange (Amberlite ® 252 resin in H⁺form, 15 cm resin height, eluant: 0.02 N HCl in each case, all fractionswere combined) Anion of a weak acid Borate Tartarate Succinate CitrateAcetate Formate Maleinate Malonate Oxalate Sample name of 292/376292/377 292/378 292/379 292/380 292/381 292/382 292/383 292/384 solutioncontaining anion Acarbose (area %) in 9.675 11.93 8.887 10.3 10.25410.597 1.633 6.89 7.351 the solution containing anions of weak acidsYield of anion 97.0 94.9 — 95.4 96.2 100.0 99.5 100.0 100.0 exchanger(%) Sample name of 289/983 298/984 289/985 289/986 289/987 289/988289/989 289/990 289/991 combined fractions after cation-exchangeAcarbose (area %) in 31.15 76.95 74.486 68.395 71.280 70.102 7.63955.437 68.533 the combined fractions after cation-exchange Yield ofcation- 7.3 82.9 — 63.4 88.2 69.1 5.9 31.0 33.6 exchanger (%) Summarizedyield of 7.1 78.6 74.2 60.5 84.8 69.1 5.8 31.0 33.6 the two steps (%)Anion of a weak acid Phthalate Benzoate Chloride Phosphate SulfateNitrate Sample name of solution 289/1001 289/1002 289/1003 289/1004289/1005 289/1006 containing anions Acarbose (area %) in the 1.609 2.15712.246 12.992 11.942 1.856 solution containing investigated anion Yieldof anion exchanger 95.8 93.9 97.3 99.1 — 97.9 (%) Sample name ofcombined 292/412 292/413 292/414 292/415 292/416 292/417 fractions aftercation- exchange Acarbose (area %) in the 34.045 80.412 51.773 69.89657.819 57.443 combined fractions after cation-exchange Yield of cation-49.4 appr. 85- 9.3 27.8 — 6.9 exchanger (%) 90 Summarized yield of the47.3 80-85 9.1 27.5 9.2 6.8 two steps (%)

What is claimed is:
 1. A process for purifying acarbose, comprising thesteps of: 1) acidifying a fermentation broth containing an acarbose; 2)removing particulates from the fermentation broth; 3) adsorbing theacarbose on a cation-exchanger in the presence of an anion of a weakacid; 4) eluting the acarbose from the cation-exchanger with at leastone of a sodium chloride solution and a salt solution; 5) precipitatingthe acarbose with a solvent; and 6) recovering the precipitatedacarbose.
 2. The process of claim 1, wherein the fermentation broth isacidified to a pH about 4 to about
 6. 3. The process of claim 1, whereinthe fermentation broth is acidified to a pH about
 5. 4. The process ofclaim 1, wherein the fermentation broth is acidified with a weak acid.5. The process of claim 4, wherein the weak acid is acetic acid.
 6. Theprocess of claim 4, wherein the weak acid is selected from the groupconsisting of tartaric acid, succinic acid, citric acid, formic acid,malonic acid, oxalic acid, phthalic acid, benzoic acid, phosphoric acidand the derivatives thereof.
 7. The process of claim 1, wherein theparticulates are removed with a filter.
 8. The process of claim 1,wherein the filter is pre-coat vacuum drum.
 9. The process of claim 1,wherein the cation-exchanger is a strong acid cation-exchanger.
 10. Theprocess of claim 9, wherein the strong acid cation-exchanger is a resinin acid form.
 11. The process of claim 1, wherein the anion of a weakacid is selected from the group consisting of tartarate, succinate,citrate, acetate, formate, malonate, oxalate, phthalate, benzoate,phosphate and the derivatives thereof.
 12. The process of claim 1,wherein the acarbose is eluted from the cation-exchanger with a sodiumchloride solution.
 13. The process of claim 12, wherein the sodiumchloride solution has a concentration of about 0.002 M to about 0.03 M.14. The process of claim 12, wherein the sodium chloride solution has aconcentration of about 0.005 M to about 0.02 M.
 15. The process of claim1, wherein the acarbose is eluted from the cation-exchanger with a saltsolution selected from the group consisting of sodium chloride,potassium chloride and calcium chloride.
 16. The process of claim 1,wherein the acarbose is eluted from the cation-exchanger with a saltsolution selected from the group consisting of sodium sulfate, potassiumsulfate and calcium sulfate.
 17. The process of claim 1, wherein theacarbose is eluted from the cation-exchanger with a salt solutionselected from the group consisting of sodium nitrate, potassium nitrateand calcium nitrate.
 18. The process of claim 1, wherein the acarbose iseluted from the cation-exchanger with a salt solution selected from thegroup consisting of sodium acetate, potassium acetate and calciumacetate.
 19. The process of claim 1, wherein the solvent used forprecipitation is selected from the group consisting of alcohols, mixtureof alcohols, acetone, acetonitrile, ester of acetic acid, ester offormic acid and ester of propionic acid.
 20. A process for purifyingacarbose, comprising the steps of: 1) acidifying a fermentation brothcontaining an acarbose; 2) removing particulates from the fermentationbroth; 3) adsorbing the acarbose on an anion-exchanger in the presenceof an anion of a weak acid; 4) eluting the acarbose from theanion-exchanger; 5) adsorbing the eluted acarbose on a cation-exchangerin the presence of the anion of a weak acid; 6) eluting the acarbosefrom the cation-exchanger with at least one of a sodium chloridesolution and a salt solution; 7) precipitating the acarbose with asolvent; and 8) recovering the precipitated acarbose.
 21. Pure acarboseas prepared in accordance with the process of claim
 1. 22. Apharmaceutical formulation comprising pure acarbose as prepared inaccordance with the process of claim 1, wherein the acarbose has apurity of at least about 94%.
 23. A pharmaceutical formulationcomprising pure acarbose as prepared in accordance with the process ofclaim 1, wherein the acarbose has a purity of at least about 96%. 24.Pure acarbose as prepared in accordance with the process of claim 20.25. A pharmaceutical formulation comprising pure acarbose as prepared inaccordance with the process of claim 20, wherein the acarbose has apurity of at least about 94%.
 26. A pharmaceutical formulationcomprising pure acarbose as prepared in accordance with the process ofclaim 20, wherein the acarbose has a purity of at least about 96%.